In the terminal portion of its journey down the arm, the median nerve passes through a congested space known as the "carpal tunnel." The walls and floor of this tunnel are formed by the carpal bones, the roof being formed by the transverse carpal ligament or the flexor retinaculum. In its passage through the tunnel, the median nerve lies crowded between the overlying ligament and the numerous flexor tendons located below and to the sides. On emerging from the tunnel, the nerve promptly divides, forming a motor branch that supplies the muscles of the thenar eminence, including the opponens pollicis, the abductor pollicis brevis, and, in part, the flexor pollicis brevis. The remaining branches carry sensation from the palmar surfaces of the thumb, index finger, long finger and the radial half of the ring finger, and from the radial half of the palm.
In 1913, Marie and Foix1 demonstrated